Cascading or tandem drawing operations with the aid of a flying pin or mandrel are known in the art, for example, through European Patent Publications EP 0,182,922 B1 or EP 0,153,495 B1, or EP 0,353,324 B1. These prior art methods have proved themselves very well in practice and are particularly useful in their application to drawing pipes of copper or copper alloys. However, extruded or cast tubular blanks have a wall thickness that is too thick for a tandem type drawing operation as disclosed in the above European Patent Publications. Thus, conventionally, extruded or cast tubular blanks are, for example, first subjected to a cold pilgrim step operation in order to further reduce the initially extruded or cast wall thickness to make the blanks suitable for the subsequent tandem drawing. However, the cold pilgrim step method is technically involved and slow, particularly where it is necessary to achieve reduced wall thicknesses suitable for a following tandem drawing operation.
It is also known to increase the diameter of tubular blanks by drawing or rolling, whereby the blank wall thickness is necessarily reduced as a result of the diameter increase. Reference is made in this connection to a book entitled "Kraft und Arbeitsbedarf bildsamer Formgebungsverfahren" (Power and Work Requirement for Plastic Shaping Methods), 1st. Ed. VEB. Deutcher Verlag fuer Grundstoff Industrie, Leipzig, .sctn.12 "Drawing and Rolling". Such diameter increasing methods do not provide any hints toward the preparation of thick wall tubular blanks for a subsequent tandem drawing. Thus, there is room for improvement in the prior art.